1. Field of the Invention
The present invention relates to an ink jet apparatus for performing the recording or printing (hereinafter typically referred to as the "recording") of characters, symbols or images (hereinafter typically referred to as the "image") by discharging the ink or functional liquid (hereinafter typically referred to as the "ink") onto the recording carrier including papers, plastic sheets, cloths, and articles (hereinafter typically referred to as the "paper"). It is meant that the ink jet apparatus referred to in the present invention may be in a variety of forms, in addition to those provided integrally or separately as the output terminal for the information processing equipment such as a wordprocessor or a computer, including a copying machine combined with an information reader, a facsimile apparatus having the information transmission and reception feature, and an equipment for textile printing onto the cloths.
2. Related Background Art
In the so-called ink jet recording apparatus which performs the printing by ejecting the ink as droplets from discharge ports onto the recording medium, pump means may be provided to expel the ink through nozzles in a head having caused a problem such as dirt mixing or drying, or fill the ink from an ink reservoir into the discharge ports before starting the printing. This pump means is represented by a piston pump having reciprocal motion of a piston as disclosed in Japanese Laid-open Patent Application No. 3-5160, and a tube pump of stroking an elastic tube with a roller as disclosed in Japanese Laid-open Patent Application No. 5-69558. The piston pump can be generally miniaturized, but has the technical difficulty in retaining the air-tightness with a sliding piston member, as well as the necessity of employing a seal member such as an O-ring to form the sealing construction, thereby tending to have too many components. On the other hand, the tube pump can retain the air-tightness with the tube itself, and is capable of flowing the ink always in one direction by stroking the tube unidirectionally, so that pump means can be constituted less expensively, but the tube length is required, amounting to the volume of content corresponding to a pump capacity, resulting in a tendency that the entire apparatus becomes larger.
Conventionally, there are following systems for driving such a pump:
1) The user manually makes the pumping as required, interlocked with an operation member.
2) A dedicated motor is provided to drive the pump.
3) A clutch mechanism is provided to connect the motor to the pump only in pumping, wherein a motor for feeding the recording medium in sub-scan direction (hereinafter referred to as a "paper feed motor") or a motor for driving the head in main scan direction (hereinafter referred to as a "carrier motor") is also utilized as a driving source.
However, the above-described conventional driving systems had the following problems.
In example 1), because of the manual operation, there are drawbacks that the pumping speed may not be stabilized to apply a predetermined pressure to the recording head, or the user can not know whether the pumping is necessary or not until the confirmation of print failure, or the operation is cumbersome.
In example 2), the pumping device as such becomes larger by the installment of a dedicated motor, and has the higher cost.
In example 3), there is also a drawback that the apparatus is inevitably complicated. This point is explained below.
For the intrinsic purpose of each motor, namely, the driving of a paper feeding roller to feed the paper for a paper feeding motor, or the driving of a carrier for a carrier motor, the control thereof is required to be very highly precise. Accordingly, it is desirable that a drive transmission system between the motor and the paper feeding roller or carrier as the driven member does not have the connection cut off. However, when driving the motor for other purposes than the intrinsic purpose, the paper feeding roller or carrier will also move. In general, in most serial printers, a carrier motor is directly connected via a belt to the carrier. In this case, the employment of the carrier motor for other purposes is difficult due to the following reasons. First, the amount of rotation of the motor in one direction is only limited to the amount of stroke over which the carrier scans. Secondly, particularly when used as a driving source for pumping, the recording head will move during the pumping, so that the connection between the pump and the recording head is difficult. Accordingly, in such printers, a paper feeding motor is used as the driving source for other purposes, in place of the carrier motor. However, an ink jet printing apparatus must usually make, besides the pumping, at least the picking-up of the recording sheet with a cut sheet feeder, wherein their operation timings are necessary to be different, so that two clutch mechanisms which can be controlled at least independently are required. Further, in order to control the clutch mechanism independently, the following mechanisms are required:
A) A solenoid or an electromagnetic clutch is used to disconnect any gear train from the motor owing to electromagnetic force.
B) A carrier is used as a selector. Namely, if the carrier is moved to a certain position, a planetary gear is forced to mesh with the gear train from the motor, whereby the carrier is mechanically associated in phase with the clutch mechanism, such that the paper feeding motor is driven to perform any task while the clutch is being connected.
C) Supposing that the direction of rotating the paper feeding roller for the feeding of the recording medium is forward, a oneway clutch is provided for transmitting a rotational force only when it is inversely rotated.
Mechanism A) takes as much cost as if a dedicated motor is installed.
Mechanism B) has a drawback that the apparatus becomes larger because the carrier must be additionally moved out of the print zone by the number of clutch mechanisms.
Mechanism C) is a simple and less costly but only allows for the allocation of one task except for the paper feeding.
As above described, conventionally, many tasks were allocated to the paper feeding motor, so that the apparatus became larger and complicated, and therefore had higher costs.
Also, when a conventional tube pump is adopted, there is a drawback that the pump itself becomes larger, as previously described. For example, as disclosed in Japanese Laid-open Patent Application No. 5-69558, when the tube is disposed in arcuate shape, and if the inner diameter of the tube is 2 mm and the pump capacity is 0.3 ml, the length of the tube is equal to 95.5 mm by dividing the pump capacity by the cross sectional area of the tube. Further, if the arcuate section of the tube is exactly semicircular, the diameter of its circle is equal to 95.5.times.2/3.14, i.e., 60.8 mm. This is considerably a larger size for the ordinary serial printer.
Referring to FIG. 1, suction recovery means using a tube pump will be described in greater detail. This suction recovery means can suck the ink by stroking a tube with a roll to produce a negative pressure (see FIG. 1). That is, a tube 301 is disposed on a base 300 of which the surface is cut out in arcuate shape, and stroked with a roll provided on the peripheral rim of a disk 302 by rotating the disk 302 having its peripheral surface placed facing closely an arcuate cut-out portion. Also, a cap holder 305 to which a rubber cap 304 is attached is movably constituted, and shifted to a capping position when a recording head 306 comes to a predefined position. That is, by rotating the disk 302 in the state where the recording head 306 is capped with the cap 304, the ink is sucked from the recording head, together with the adhering matter around discharge ports.
Although duplicated with previously described ones, the problems with conventional suction recovery means of such a constitution are summarized as below.
(1) To say nothing of the cases of providing a dedicated motor to drive the tube pump, in the cases where the driving of tube pump is taken from a driving source for the paper conveying roller, reverse flow preventing means for preventing the reverse flow of the ink, or drive transmission switching means, may be required, leading to the increased cost.
(2) In order to assure the amount of ink suction necessary and sufficient to recover an ink jet head clogged, it is necessary to control the amount of stroking the tube 301 by recognizing the position of the roll 303. Also, if the tube 301 is blocked when the ink jet head 306 is capped, a positive pressure may instantaneously occur to cause the ink within the nozzles to flow back toward a supply chamber, in some instances, whereby the recognition of the roll position is also required. Thus, for example, sensing means 307 such as a photo-sensor as shown in FIG. 11 is required, also becoming a factor of the increased cost.